Method and apparatus for detecting angular defects in a tubular member

ABSTRACT

A method and apparatus for determining the extent of defects in tubular elements for use in an oil or gas well is disclosed. The apparatus includes an electromagnetic or other suitable inspection device, cooperating with longitudinal and circumferential position detectors for determining the position and configuration of all defects within a tubular member. Signal generating means are provided for producing signals corresponding to the configuration, longitudinal position, and circumferential position of the defects located within the wall of the tubular member. The signals are processed, preferably by a computer, so that the presence, nature, and precise location of each defect is determined and visually displayed at a suitable display means. Display means are provided for generating a two-dimensional visual display wherein the circumferential and longitudinal positions of the defects are selectably displayed.

This is a division of application Ser. No. 424,136 filed 10/19/89.

BACKGROUND OF THE INVENTION

1. Field

This invention relates to defect inspection of tubular elements, andmore particularly to displaying the results of such defect inspection ina readily usable format.

2. Description of the Prior Art

Continuous tubular strings formed of connectable tubular sections orelements, such as production tubing strings, drill pipe strings andcasing strings, are used in the drilling, completion and production ofsubterranean oil and gas wells. The individual tubular elements, whichare typically steel castings, frequently contain manufacturing defectssuch as seams, laps, inclusions, and gouges which could result in costlyfailures if undetected prior to installation. Therefore, tubularelements are commonly inspected at the point of manufacture so that anyserious defect can be located and repaired, if possible, before thedefective tubing is shipped to the well site.

Tubular elements are also subject to various forms of mechanical damageafter being installed within a well. It is therefore advantageous thatthe individual tubular elements comprising a tubular string be inspectedperiodically. Typically, the inspection of tubular sections occurs afterthe individual sections comprising the tubing string have been removedfrom the well and disengaged. Defect inspections are conventionallyperformed on a section by section basis.

A number of techniques exist for determining the presence of a defect ina tubing section. For example, the location of internal and externalradially extending and three-dimensional defects, including sluginclusions, mechanical damage, pitting and fatigue cracks, has beendetermined by flux leakage techniques in which a longitudinal magneticfield is induced by one or more magnetic induction coils. External fluxdetectors are located around the tubing and the maximum signal isrecorded to locate the defect. Similarly, longitudinal defects may bedetected magnetically by the "rotating pole" method, where the magneticfield is applied from the outside by rotating electromagnets, and fluxdetectors positioned between the poles scan the outside surface of thepipe. Various techniques relating to electromagnetic inspection are wellknown in the art with a list of examples being set forth in thefollowing patents:

    ______________________________________                                               4,492,115     4,636,727                                                       4,555,665     4,698,590                                                       4,578,642     4,704,580                                                       4,611,170     4,710,712                                                       4,629,985     4,715,442                                                       4,629,991     4,792,756                                                ______________________________________                                    

While electromagnetic inspection systems have become widely accepted inthe industry, various other techniques are also available and may evenbe preferable depending on the circumstances. Such other inspectiontechniques include the use of radiation as set forth in U.S. Pat. Nos.3,835,323 and 3,855,465. Also known in the art, but less frequentlyutilized, are ultrasonic inspection systems.

Any of the above mentioned inspection techniques may be utilized toadequately detect the presence of defects located within the wall oftubular elements. The most essential function of existing inspectiondevices is to generate an electrical signal containing informationregarding physical characteristics such as defects and otherirregularities in a given segment of a tubular member, and to displaysuch information in a useful manner. Typically, the display consists ofa strip chart generated on a strip recorder, indicating theaforementioned electrical signal in analog form with a graphicindication for each irregularity sensed by the detecting device. Aninspection crew then utilizes the graph as a guide to visually confirmthe existence of serious defects which would result in the rejection ofthe tubular element being inspected. Conventional graphic displays,however, are severely limited in their ability to convey usefulinformation to the inspection crew responsible for visually locatingdefects.

A conventional strip chart display provides a very general indication ofthe existence of a defect and its longitudinal position along the lengthof a tubular member. The existence of a defect is indicated by one ormore vertical peaks in the graph, while the longitudinal positionroughly corresponds to the location of the peak (or peaks) along thehorizontal axis. If the display contains a plurality of closely adjacentpeaks, conventional systems do not distinguish between several closelyadjacent defects, a single large defect, or several defects at the samelongitudinal position but spaced apart circumferentially. In fact, withrespect to the third situation, conventional systems provide virtuallyno useful information to the inspection crew regarding thecircumferential location of any defects. In short, conventional displaysprovide no usable information regarding the shape, size or amplitude ofa defect, and only minimal information regarding the location.

The absence of circumferential position indications in conventionalgraphic displays becomes an even greater problem when the tubing to beinspected contains a longitudinal weld seam. Since a seam is essentiallya continuous irregularity extending from one end of the pipe section tothe other, it appears on a conventional graphic display as a continuousstring of defects indicated by a solid line of peaks. As such, the weldseam indications on the graphic display completely overshadow all otherindications, thus making it virtually impossible to distinguish the weldseam from the defects.

In addition to the imprecise defect locating capabilities of prior artsystems, conventional inspection devices typically employ band passfilters to remove extraneous information, such as the presence ofcertain non-defect irregularities, from the incoming signal. Thistechnique is effective for the intended purpose, but the informationfiltered out is permanently lost. Conventional systems do not allow theuser thereof to include all extreme signal values in the display, if sodesired.

SUMMARY OF THE INVENTION

The present invention addresses the deficiencies in prior art inspectionsystems, including those set forth above. Specifically, the method andapparatus disclosed herein are used to determine the extent of defectsoccurring in a tubular member, such as a section of tubing used in anoil or gas well, and visually display such defects in a greatly improvedmanner. A tubing inspection head detects the physical characteristics ofa tubular member and generates an electrical signal correspondingthereto. Included in the physical characteristics are defects, and thecorresponding electrical signals indicate the presence, angularorientation, and overall configuration of such defects. Additionally,longitudinal and circumferential position detectors generate signalsindicating the longitudinal and circumferential position of theinspection head as it moves from one end of the tubular member to theother. A computer receives the signals generated by the inspection headand the longitudinal and circumferential position detectors, correlatesthe signals to obtain an accurate set of defect data including the size,configuration, orientation, longitudinal position, and circumferentialposition of every defect within the tubular member. Some or all of thedefect data may then be displayed in a two-dimensional format on one ormore visual display means.

The computer program utilized to process the signals and display thedefect data provides a great deal of flexibility for the presentinvention. The degree to which the incoming signals are filtered may beselected as desired thus providing for a greater or lesser degree ofaccuracy as warranted by the situation. The computer program alsoprovides the capability of selectively tailoring the visual display suchthat various kinds of defects may be emphasized or de-emphasized asdesired.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features of the present invention will become morereadily apparent from the following detailed description, when read inconjunction with the accompanying drawings, in which:

FIG. 1 is a simplified, functional block diagram of the preferredembodiment of the system of the present invention;

FIG. 2 is a simplified, functional, block diagram of the embodiment ofFIG. 1, showing additional features of the preferred circumferentialposition detector;

FIG. 3 is a strip chart representative of the defect displayingcapability of prior art inspection systems;

FIGS. 4a-4d are examples of the preferred graphical and two-dimensionaldefect displays produced using principles of the present invention;

FIG. 5 is an example of an alternative defect display in tabular formproduced using principles of the present invention; and

FIGS. 6a-12 are a simplified flowchart of the main computer program andkey subroutines which perform the signal processing functions for thepreferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 provide schematic depictions of the preferred system forcarrying out principles of the present invention, with FIG. 2emphasizing certain features of the preferred apparatus. Referringinitially to FIGS. 1 and 2 principles disclosed herein are preferablyembodied in system 10, which generally consists of inspection head 12,circumferential position detector 14, longitudinal position detector 16,a central processing unit or computer 18, and a variety of visualdisplay devices collectively identified by the numeral 20. While it ispreferred that system 10 include a CRT 20a, chart recorder 20b, plotter20c, and printer 20d, it is only necessary for system 10 to include someform of visual display compatible for use with computer 18. It will beunderstood by those skilled in the art that any number of conventionalvisual display devices may be suitable for the purposes of the presentinvention.

As illustrated, system 10 may be effectively employed to accuratelydetermine the extent of defects in a tubular member 22, and visuallydisplay the defects in great detail on display device 20. Tubular member22 typically consists of a single section or joint of pipe associatedwith oil and gas wells. System 10 may also be incorporated into anon-site inspection facility, wherein an entire tubing string may beconveniently inspected during removal from the well bore. Regardless ofwhether system 10 is intended for on-site or off-site inspection, themost significant physical requirement is that tubular member 22 andinspection head 12 be movable relative to one another along thelongitudinal axis of tubular member 22 to insure complete inspection oftubular member 22 from one end to the other. Typically, off-siteinspection, system 10 would include inspection head 12 mounted in alaterally fixed position with tubular member 22 longitudinally movabletherethrough by means of a conveyor. For on-site inspection, on theother hand, system 10 would have inspection head 12 vertically fixedabove the well bore, and tubular member 22 would be drawn upwardlytherethrough during removal from the bore.

During operation of system 10, inspection head 12 comprises the meansfor generating a defect signal 24, which includes a variety ofinformation about the physical characteristics of tubular member 22.Included in this information are the identification and configuration ofany and all defects located within the body of tubular member 22. At anygiven instant during the operation, inspection head 12 is generating adefect signal 24 representing the characteristics of a single discretesolid segment of tubular member 22. By suitably moving inspection head12 from one end of tubular member 22 to the other, the content of defectsignal 24 is broadened to include information regarding the entire solidvolume of tubular member 22, the entire solid volume consisting of theaggregate sum of all discrete solid segments.

As inspection head 12 moves longitudinally relative to tubular member22, circumferential position detector 14 and longitudinal positiondetector 16 generate circumferential signal 26 and longitudinal signal28, respectively, which contain information indicating the location ofthe defects detected by inspection head 12. Signals 24, 26, and 28 arethen directed into computer 18, which utilizes conventionalmicroprocessor circuitry to correlate the signals, thus obtaining auseful set of data concerning the presence, configuration, angularorientation, and precise location of the defects within tubular member22. This data, referred to herein as "defect data", is then displayedeither in its entirety or in selected portions on one or more of thevisual display devices 20. Illustrative examples of the visual displayprovided by the principles of the present invention are set forth inFIGS. 4a-4d and FIG. 5.

Those skilled in the art will recognize that signals 24, 26, and 28 willbe generated as analog signals of varying voltages, and must beconverted to corresponding digital signals prior to processing bycomputer 18. It will also be understood that certain filtering networksmay be employed in order to effect such conversions. High pass or lowpass filters, however, are not necessary to segregate defect data fromnon-defect data within defect signal 24 due to the unique signalprocessing features of the present invention, discussed in greaterdetail below. Of course, defect signal 24 may be segregated byconventional band pass filters without departing from the scope of thepresent invention. As used herein, defect data relates to thoseirregularities which would result in the rejection of tubular member 22,while non-defect data relates to less severe irregularities which wouldnot result in such a rejection.

Since defect signal 24 generally contains an enormous volume ofinformation, only a portion of which relates to actual defects, it isnecessary to selectively reduce the volume of information so the memorycapacity of computer 18 is not exceeded. Rather than applying aconventional low-pass filter to screen out the frequencies normallyassociated with non-defect irregularities, the present inventionincludes certain programming steps to enable computer 18 to distinguishdefect information from non-defect information. After defect signal 24has been digitized, the numerical values contained therein are comparedby computer 18 to a threshold number selected by the user. The thresholdis typically one and one-half times the average numerical value ofdigitized defect signal 24, but is may be varied as desired depending onthe defect tolerances of the user. Computer 18 operates to discard alldata having a numerical value less than the threshold, and record theremainder for further processing.

The present invention represents a unique combination of inspection head12 with circumferential position detector 14 and longitudinal positiondetector 16, and the principles of this invention are intended to applyregardless of the precise embodiment of these components. In particular,inspection head 12 is preferably intended to be an electromagneticdetection device, such as that disclosed in U.S. Pat. No. 4,710,712, butthe teachings of this invention are equally applicable for use with aradiation inspection apparatus, an ultrasonic inspection apparatus, orany other inspection apparatus capable of generating a suitable defectsignal 24. For purposes of carrying out the principles of the presentinvention, the entire specification of U.S. Pat. No. 4,710,712 is herebyincorporated by reference and made a part hereof. The interchangeabilityof various types of inspection heads will be fully appreciated by thoseskilled in the art.

The preferred apparatus for carrying out the principles of thisinvention includes two detector head segments 13, each of which containstwenty-four detecting coils and/or probes for detecting magnetic fluxleakage. Therefore, defect signal 24 preferably consists of themultiplexed signals from forty-eight separate flux detectors, each ofwhich is generating a signal, at any given instant, indicative of thedefects in a separate discrete solid segment of tubular member 22. It isconceivable, however, that any number of flux detectors could beemployed for the purposes disclosed herein. It is understood in the artthat a large number of relatively small flux detectors effectivelydivides tubular member 22 into a greater number of discrete solidsegments, thus improviding the resolution of the visual displayappearing on display device 20.

In the preferred embodiment of the present invention, circumferentialposition detector 14 is a magnetic sensor which detects each rotation ofinspection head 12, by means of magnet 30 which is secured thereto asillustrated in FIG. 2. As such, position detector 14 serves as thesensing means for revolution counter 32, which simply provides computer18 with a signal 26a indicating the passing of each revolution. Tocomplete the information needed for determining circumferentialposition, clock 34 and angle counter 36 provide timing signal 26b whichis conventionally combined with signal 26a by computer 18 to calculatethe rotational position of inspection head 12 at any given instant.Computer 18 then correlates this information with the defect datatransmitted by defect signal 24 and the longitudinal positiontransmitted by longitudinal signal 28 and displays the results ondisplay devices 20 as set forth herein. For convenience and simplicity,revolution counter signal 26a and angle counter signal 26b arecumulatively referred to as circumferential signal 26.

Alternatively, circumferential position detector 14 may consist of anysuitable apparatus for determining the circumferential position of thedefect detector and generating a corresponding circumferential signal26. It is expected that with certain "fixed-head" defect detectors, thecircumferential position of defects will be indicated by the defectdetector itself, and a separate circumferential position detector 14 maybe eliminated altogether.

Longitudinal position detector 16 preferably consists of a wheelrotatably secured to a rigid support member such that its outer edgesurface bears against the outer surface of tubular member 22. As thewheel of position detector 16 rolls longitudinally along the entirelength of tubular member 22, a transducer connected to the wheelgenerates longitudinal signal 28 which generally corresponds to thedistance traveled by the wheel, thus providing computer 18 withsufficient information to determine the longitudinal position ofinspection head 12 and any defects detected thereby.

To best illustrate the features and advantages of the present invention,it is helpful to start with a typical visual display as provided by theprior art. FIG. 3 is a reproduction of such a display, a strip chartproduced on a chart recorder by an electromagnetic inspection systemutilizing two detector head segments in a rotating detector apparatus,each head segment generating a separate line on the graphic display.Horizontal axes 38 and 40 each contain a graphic indication of thesignal generated by each of the two head segments, with the distancebetween points A and B corresponding generally to the length of thetubular member inspected. Vertical elements 42 indicate irregularitieslocated within the body of the tubular member, with the longer elements,such as peaks 42a, indicating the most likely presence of a defect. Thelocation of peaks 42a along the horizontal axes 38 and 40 indicate thegeneral longitudinal location of the defects, but the size,configuration, and angular orientation of the defects must be determinedby visual inspection. Furthermore, the presence of defects must bevisually determined as well, due to the high incidence of false readingsand the inability to distinguish between true and false readings. Theuncertainty in reading a conventional graphic display is compounded bythe overlapping coverage provided by the two detector head segments asthey rotate around the pipe.

While most of the tubing presently in use in the oil and gas industrycontains no longitudinal seam, there will be occasions from time to timewherein welded tubing containing a longitudinal seam must be inspected.Conventional graphic displays have proven to be inadequate fordisplaying the results of such inspections, since the presence of thecontinuous longitudinal seam completely dominates the graphic display tothe extent that the display is nothing but a continuous series of peakswhich overshadow any indications of defects.

In stark contrast to the crude printout produced by prior art methodsand devices, FIGS. 4a-d represent examples of the highly informativegraphic displays made possible by the teachings of the presentinvention. The examples shown may either be observed on a CRT screen, orreproduced on a printer, plotter, or chart recorder. Referring initiallyto FIG. 4a, it can be seen that the unique function of the presentinvention yields a two-dimensional map 44 of the defects located withintubular member 22. Preferably, map 44 includes a horizontal axis 46corresponding generally to the longitudinal length of tubular member 22,and vertical axis 48 corresponding to the circumference of tubularmember 22, with the graduation marks along vertical axis 48 signifyingdegrees of rotation from a pre-selected 12 o'clock position. Forpurposes of calibrating map 44 with tubular member 22, the twelveo'clock position is noted prior to inspection. Defect identifiers 50a-findicate the presence, configuration, longitudinal position, andcircumferential position of each defect located throughout tubularmember 22. When viewed on a CRT screen, defect identifiers 50a-fconstitute groups of one or more pixels.

For the sake of convenience and to suit the needs of a particularcustomer, the defect identifiers may be classified by the relative sizeof their corresponding defects. Accordingly, defect identifiers 50a, band c indicate the presence of short defects, 50d indicates the presenceof a long defect, and 50e and f indicate the presence of defects havingangular orientations, or angle defects. The designations "short","long", and "angle" are relative terms as used herein, and do notcorrespond to any particular absolute dimensions of size. Thesignificance of these terms will become apparent in light of theadditional features of the preferred embodiment as discussed below.

Positioned immediately beneath map 44 is graph 52, indicating agraphical representation of the signals received from the two headsegments 13 of inspection head 12. Rather than indicating the analogsignal as with prior art devices, graph 52 depicts the digitized versionof defect signal 24 after processing by computer 18. As such, graph 52is a much more accurate representation of the actual state of defectswithin tubular member 22.

In the preferred formats shown, the far right-hand side of the displaycontains certain information regarding the parameters of the procedureand the physical characteristics of the tubing being inspected. Inaddition to the display mode, this section indicates the threshold valuefor the display, the rotational velocity (in RPM's) of the inspectionhead 12, the percentage of coverage provided by the inspection head 12,and the outside diameter, wall thickness, and grade of tubular member22. Of course, this section of the display may be altered as desiredwithout departing from the principles of this invention.

In order to selectively filter out false or non-defect indications inmap 44, graph 52 includes threshold line 54 which may be set or alteredaccording to the particular needs of the customer. The threshold valuerepresented by line 54 serves as a computer generated high pass filterwhich only allows those values greater than the threshold to appear asdefect identifiers on map 44. In the preferred display shown, thethreshold value setting is indicated with the information shown to theright of map 44 and graph 52.

In addition to the threshold value setting, the information shown at theextreme right of FIGS. 4a-d includes the mode selected for theparticular display. For the examples shown, FIG. 4a represents a displayin the inspection mode, FIG. 4b represents the same display in the setup short mode, FIG. 4c represents the same display in the set up anglemode, and FIG. 4d represents the same display in the set up long mode.Essentially, FIG. 4a is the cumulative version of FIGS. 4b, c, and d, inwhich short defects, long defects, and angle defects are givensubstantially equal prominence. In FIG. 4b, on the other hand, theselection of the set up short mode by the user results in additionalprocessing being performed by computer 18 so that short defects areemphasized, with long and angle defects being omitted or shown in adistorted fashion. For example, in FIG. 4b short defect identifiers 50a,b, and c, appear more clearly than in FIG. 4a, whereas long defectidentifier 50d appears in broken form and angle identifiers 50e and f donot appear at all. Similarly, in FIG. 4c angle defect identifiers 50eand f are clearly displayed, but short defect identifiers 50a, b, and chave disappeared and long defect identifiers 50d appears broken.Finally, FIG. 4d reveals how long defect identifier 50d is emphasizedwhile short defect identifier 50a and angle defect identifiers 50e and fare not shown. The programming steps necessary to isolate the differenttypes of defects and produce the different displays shown in FIGS. 4a-dprovide a higher degree of defect identification than is presently knownin the industry.

With the preferred embodiment of this invention, it is also possible todisplay the defect data in tabular form as shown in FIG. 5. The table ofFIG. 5 includes four columns of information reflecting the physicalcharacteristics of the defects in tubular member 22. The characteristicshown for each defect are the longitudinal position, the circumferentialposition, longitudinal or axial length, and the angular orientation. Thecolumns entitled longitudinal and traverse are grouped together underthe heading "Location", and the columns entitled "Axial" and "Orient"are grouped under the heading "Estimation". The presentation of defectdata in this manner provides a convenient tool for assisting theinspection crew in visually locating each defect. In addition to thefour columns of defect data, the preferred table also includes a fifthcolumn headed "joint number" for identifying the section or joint oftubing being inspected, and a sixth column headed "Comment" may beprovided in which the inspection crew may record notes as desired.

To illustrate the convenience of the tabular display set forth in FIG.5, the appropriate line of data corresponding to long defect identifier50d has been highlighted and designated by the numeral 55. Upon readingthe defect data set forth in line 55, the inspection crew knows that adefect approximately 11.4 inches long may be found, starting at a point14.91 ft. (or 14 ft. 10 in.) from the leading edge of pipe joint No. 1,located at circumferential position 6:39 and extending essentiallyparallel to the longitudinal axis of the tubular member. Armed with thisknowledge, the inspection crew can relatively easily locate the defectcorresponding to identifier 50d, and determine whether the affectedsection of tubing should be repaired or replaced.

As noted above, the table illustrated in FIG. 5 includes a columnspecifying the angular orientation of each defect identified. Theangular orientation is calculated by computer 18 based upon informationcontained in defect signal 24, in combination with other known data. Asinspection head 12 rotates around tubular member 22 at a constantrotational velocity, defect signal 24 indicates the presence of aplurality of discrete points which, when viewed in their entirety,indicates the presence of an angle defect such as those indicated at 50eand f shown in FIGS. 4a and c. Since an angle defect is, by definition,positioned at an angle with respect to the longitudinal axis of tubularelement 22, the detection of two adjacent discrete points on a givenangle defect will require slightly more, or slightly less, than onecomplete revolution of inspection head 12. This phenomenon results in atime differential, or time lag, between the detection of adjacent pointson an angle defect and the period of rotation of inspection head 12.Computer 18, being pre-programmed with the rotational and longitudinalvelocity of inspection head 12, can then apply conventional mathematicalprinciples to determine the angular displacement of a first point from asecond point on an angle defect, the angular displacement typicallybeing determined with reference to the longitudinal axis of tubularmember 22. The angular displacement between two discrete points on thedefect is thus displayed in FIG. 5 as the angular orientation of thedefect.

FIG. 6a through FIG. 12 illustrate a flowchart for the computer programdeveloped to perform the various signal processing functionsincorporated into the preferred embodiment of the present invention.While the illustrated flowchart describes the preferred software forcarrying out the principles of this invention, it will be understood bythose skilled in the art that substantial changes may be made in thecomputer program without departing from the scope of the invention.

As disclosed herein, the flowchart depicting the preferred programconsists of a main program illustrated in FIGS. 6a-c, and six keysubroutines illustrated by FIGS. 7a-d, FIG. 8, FIGS. 9a-e, FIG. 10,FIGS. 11a-b, and FIG. 12. A general description of each of thesesections is set forth below, followed by a more detailed discussion ofthe preferred program.

FIGS. 6a-c represent the main program which sets up the overallframework for performing the processing tasks necessary to receive,process, and display data as discussed herein. The main programflowchart 56 illustrates the preferred sequence for identifying thevarious parameters involved in the procedure, allocating sufficientmemory to store the necessary data, and assigning a subroutine or otherfunction to be performed by certain function keys and commands.

FIGS. 7a-d set forth flowchart 58 which represents a subroutineidentified as "demux₋₋ adc". The function of the demux₋₋ adc program isto enable the computer 18 to receive and store information contained indefect signal 24, circumferential signal 26, and longitudinal signal 28.The preferred program set forth in flowchart 58 is designed toaccommodate a defect signal 24 comprising 48 separate channels,corresponding to the 48 defect detectors included in the preferredapparatus.

FIG. 8 contains flowchart 60 which represents the "inspl₋₋ cmd"(inspection command) subroutine. This subroutine operates to retrievethe defect data from storage and display the data in the inspection modeas illustrated in FIG. 4a and discussed above.

Flowchart 62, as shown in FIGS. 9a-e, discloses a subroutine labeled"insp₋₋ cmd()". This portion of the program allows the user of thesystem to select either short, long, angle, or inspection modes for thetwo-dimensional display, as discussed above, and also to enhance thedisplay for specified portions when desired. The "insp₋₋ cmd()"subroutine utilizes the cursor, appearing as the point of intersectionbetween perpendicular x and y axes, to focus on any given pointappearing on the two-dimensional display. By selectively moving the xand y axes so that the cursor coincides with a given defect, the usercan determine the precise longitudinal and circumferential position ofthe defect on the two-dimensional map.

The "insp₋₋ cmd()" subroutine identified by flowchart 62 also provides a"screen zooming" feature which yields an enlarged display of a portionof the two-dimensional map, as mentioned above. This feature allows theuser to view a particular longitudinal section of tubular member 22 ingreater detail simply by designating the longitudinal boundaries of therelevant section. For example, if the user desires to see an explodedview of a central portion of tubular member 22 lying between 10 feet and20 feet, the user can make appropriate designations at the 10 and 20foot points and the computer program will expand that portion of thedisplay to fill the entire two-dimensional map.

The subroutine entitled "graph₋₋ insp", identified by flowchart 64 inFIG. 10, serves the linking function of correlating the longitudinalposition of the defect data with the corresponding position on thetwo-dimensional map for purposes of carrying out "screen zooming".Additionally, this subroutine calls a "map₋₋ 2d" subroutine into play todisplay the defect data on a CRT screen.

The "map₋₋ 2d" subroutine mentioned above is disclosed in flowchart 66illustrated in FIGS. 11a and b. This subroutine operates to correlatethe defect, longitudinal, and circumferential signals to determine theposition of each defect, and generate a pixel on the CRT screen tovisually display each defect in its proper location. When creating thevisual display, this subroutine calls upon the "diff" subroutine whichadjusts the display according to the mode (short, long, angle, orinspection) selected by the user.

Flowchart 66 illustrated in FIG. 12 sets forth the framework for the"diff" subroutine mentioned above. This subroutine performs the signalprocessing functions necessary to distinguish the various types ofdefects based upon size and angular orientation, thus providing for thedifferent display modes discussed herein.

DETAILED DESCRIPTION OF COMPUTER PROGRAM

In order to carry out the principles of the present invention utilizingthe preferred program for this purpose, identified schematically asflowchart 56, the first step is to initialize the parameters governingthe process (box 56-1). At this stage in the inspection procedure, theuser establishes the various operating frequencies and threshold valuesneeded for subsequent calculations. Also established at this stage arethe pipe speed, detector gain, inspection head rotational velocity, andthe length, outside diameter, and wall thickness of the pipe to beinspected. After all necessary operating parameters have beenestablished, a sufficient block of memory is allocated to store the realtime data input from signals 24, 26, and 28 (box 56-2).

Once the internal functions and parameters have been initialized and thememory is properly allocated, the main program instructs the computer torun various subroutines and functions in response to certain entries(box 56-3). The operations automatically performed upon selection offunction keys F1-F10 are assigned as follows:

F1 calls the inspl₋₋ cmd subroutine, displayed in FIG. 8 as flowchart60, which assigns a flag value to indicate the acquisition of new dataand further calls the insp₋₋ cmd() subroutine for generating thetwo-dimensional display (boxes 56-4 and 56-5);

F2 calls a dsp₋₋ cmd subroutine which simply displays the raw real timedata (boxes 56-6 and 56-7);

F3 calls the inspl₋₋ cmd subroutine, illustrated as flowchart 60 in FIG.8 which generates the two-dimensional display map for inspection (boxes56-8 and 56-9);

F4 calls a para₋₋ cmd subroutine which allows the user to change theparameters as desired (56-10 and 56-11);

F5 calls an rpm₋₋ cmd subroutine which displays the rotational velocityof the rotating inspection head 12 (56-12 and 56-13);

F6 calls the det₋₋ offset₋₋ cmd subroutine which allows the user to setthe required offset for each detector channel (56-14 and 56-15);

F7 calls a set₋₋ ch₋₋ cmd subroutine which allows the user to select themultiplexer output value for each detector channel (boxes 56-16 and56-17);

F8 calls a set₋₋ samp₋₋ phres₋₋ cmd subroutine which allows the user toset the sampling threshold (boxes 56-18 and 56-19);

F9 calls the save₋₋ cmd subroutine which operates to save the datareceived through input signals 24, 26 and 28 (boxes 56-20 and 56-21);

F10 calls the help₋₋ cmd subroutine which generates a help menu on thescreen (boxes 56-22 and 56-23);

"Read" command calls the read₋₋ cmd subroutine which allows the user toread raw data directly from the file (boxes 56-24 and 56-25);

"DOS" command sets the computer up to perform conventional DOS commands(boxes 56-26 and 56-27); and

the "ESCAPE" key returns the computer to DOS format (box 56-28).

The order of the steps performed by the main program illustrated inflowchart 56 constitutes a convenient, logical progression for creatingthe framework for the overall programming including all subroutines. Itwill be understood by those skilled in the art, however, that theprecise order of steps is, in many instances, simply a matter of choice,and may be rearranged considerably without departing from the teachingsof the present invention.

The demux₋₋ adc subroutine, illustrated by flowchart 58 in FIGS. 7a-d,constitutes the heart of the signal processing features, wherein signals24, 26, and 28 are received and stored. As with virtually any computerprogram, the first step comprises initializing the parameters necessaryfor performing the operations specified by the remainder of thesubroutine (box 58-1). In addition to the parameters previously selectedfor the main program, the demux₋₋ adc subroutine further requires theinitialization of the values corresponding to revolution counter signal26a and angle counter signal 26b (box 58-2).

The demux₋₋ adc subroutine next directs the computer to read the defectssignal 24 for each of the 48 detector channels, with gain and offsetbalanced (box 58-3), as well as revolution counter signal 26a, anglecounter signal 26b, and longitudinal signal 28 (box 58-4). The period ofrotation for inspection head 12 is then established by determining theangle counter reading corresponding to a single revolution of the tooltrip head 12 (boxes 58-5 and 58-6).

The demux₋₋ adc subroutine then performs the signal processing functionsnecessary for the real time screen output and chart recorder output.Initially, the maximum value of the forty-eight channels comprisingdefect signal 24 is determined (box 58-7) and processed by a digitalhigh pass filter (box 58-8). If the maximum value is less than thepre-set threshold value, the output maximum value (out₋₋ max48ch) is setat zero (boxes 58-9 and 58-10). The signal difference for each fluxdetector is then established (boxes 58-11 and 58-12), with the maximumvalue being processed by a digital band pass filter (box 58-13). If theresulting value (out₋₋ dif) is less than a given threshold, the value isset at zero (boxes 58-14 and 58-15).

After the out₋₋ max48ch and out₋₋ dif parameters have been determined,the amplitude of out₋₋ dif is displayed on the CRT screen in real time(box 58-16), and the values of both parameters are converted into analogsignals and sent to a two channel strip chart recorder (box 58-17). Thecomputer then determines if the raw data should be stored or discarded(boxes 58-18 and 58-19), and the data acquisition sequence is continued,if necessary, with the data record being updated accordingly (boxes58-20 and 58-21).

The inspl₋₋ cmd subroutine referred to above is identified by flowchart60 set forth in FIG. 8. This subroutine serves initially to assign avalue of 1 to the insp₋₋ mode variable "inspect mode", and create a flagto signal the acquisition of new data (box 60-1). This is a preliminarystep essential to the operation of the insp₋₋ cmd() subroutine, which isalso called into play by the inspl₋₋ cmd subroutine (box 60-2) as setforth in more detail below.

The insp₋₋ cmd(), identified generally as subroutine 62, requires thatadditional parameters be initialized before performing the operationspecified therein (box 62-1). Next, relying upon an instructionpreviously supplied by the inspl₋₋ cmd subroutine, new data isautomatically acquired if the insp₋₋ mode value equals 1 (boxes 62-2 and62-3). Regardless of whether or not new data is acquired, the insp₋₋mode is reset to zero and a suitable display record is set up toindicate the length of tubing corresponding to the required data (box62-4). The computer next determines if all the acquired data records("acq₋₋ rec") have been received and, if not, the user is instructed todepress the F1 key to acquire new data (box 62-5). If all data has beenreceived, the graph₋₋ insp subroutine is called to generate atwo-dimensional map and display the records thereon (box 62-6).

The next series of operations performed by the insp₋₋ cmd() subroutineprovide the on-screen focusing feature which allows the user to pinpointthe location of the defects appearing on the two-dimensional map. Afterall the data is properly displayed on the two-dimensional display, thetext₋₋ insp subroutine is called and the cursor position is shown as theintersection between x and y axes (box 62-7). The user is then able toaccurately position the cursor by moving the x and y axes by depressingthe correct key on the keyboard (box 62-8).

In the preferred embodiment illustrated, the "left cursor" key serves tomove the x axis left (boxes 62-9 and 62-10), the "right cursor" keymoves the x axis right (boxes 62-11 and 62-12), the "up cursor" keymoves the y axis upwardly (boxes 62-13 and 62-14) and the "down cursor"key moves the y axis downwardly (boxes 62-15 and 62-16). Finally, theuser has the option of regenerating the screen simply by depressing the"HOME" key (boxes 62-17 and 62-18), or exiting the subroutine bydepressing the "ESCAPE" key (box 62-19).

The insp₋₋ cmd() subroutine allows the user to vary the display modebetween short, long, angle, and inspection modes, and regenerate thetwo-dimensional map accordingly, as discussed above. The program assignsa numerical entry corresponding to each different mode, as follows: ifthe numeral "1" is entered, the two-dimensional map is regenerated inthe angle mode (boxes 62-20 and 62-21); if the numeral "2" is entered,the map is regenerated in the short mode (boxes 62-22 and 62-23); if thenumeral "3" is entered, the map is regenerated in the long mode (boxes62-24 and 62-25); and if the numeral "4" is entered, the map isregenerated in the inspection mode (boxes 62-26 and 62-27).

This subroutine also assigns functions to various letters of thealphabet to provide additional features which may be helpful to the userof the system. As illustrated, the selection of the letter "R" calls areport₋₋ reject subroutine which generates the defect summary shown inFIG. 5 (boxes 62-28 and 62-29). Selection of the letters "S", "F", or"V" varies the speed of the cursor movement from slow, to fast, to veryfast, respectively (boxes 62-30 through 62-35).

Selection of the letter "P" instructs the computer to plot thetwo-dimensional display map on an attached plotter (boxes 62-36 and62-37). If the user desires to change the threshold value to increase ordecrease the amount of information being displayed, the letter "T" maybe selected (boxes 62-38 and 62-39). Entry of the letter "M" allows theuser to select a completely different analysis algorithm, assign acorresponding channel half width value (ch₋₋ half₋₋ width), andregenerate the two-dimensional display map in accordance with the newalgorithm (boxes 62-40 and 62-41).

The user of system 10 can quickly check the high pass and low passfilter values for the digital filters included in the chart recorderoutput by entering either the letter "H" or "L", respectively (boxes62-42 through 62-45). Finally, by entering the letter "Z", the user canutilize the screen zooming feature discussed above, wherein the first"Z" entry marks the initial longitudinal boundary and the second "Z"entry marks the final longitudinal boundary for the enlarged view (boxes62-46 and 62-47).

In order to avoid confusion and erroneous displays, the insp₋₋ cmd()subroutine automatically checks the positions of the x and y axes toinsure that both are within the range of the two-dimensional displayshown on the screen (box 62-48). In the event that one or more of thepreviously described functions has been performed, thus temporarilyremoving the two-dimensional display map, the cursor is thenre-displayed as the intersection of x and y axes (box 62-49).

The graph₋₋ insp subroutine referenced at box 62-6 is illustrated asflowchart 64 in FIG. 10. Additional parameters must first be initialized(box 64-1) in order for the computer to perform the correlatingfunctions of this subroutine. After the necessary parameters have beenestablished, the axial, or longitudinal, display positions on the CRTscreen are correlated to the defect data points contained in the datarecords for purposes of the screen zooming feature discussed above (box64-2). After this correlation, or mapping, procedure has begun, themap₋₋ 2d subroutine is called upon to display the data on the CRT screen(box 64-3) while the correlation continues until completed (box 64-4).

The map₋₋ 2d subroutine referred to above is illustrated as flowchart 66in FIGS. 11a and b. As with certain other subroutines, this portion ofthe program requires that new parameters be initialized before anyadditional processing is performed (box 66-1). The processing functionsof this subroutine are essentially contained within a logic loop,wherein the computer first determines if all the records are beingdisplayed (box 66-2), and, if so, the maximum defect value for each ofthe two detector head segments 13 is displayed on the screen (box 66-8).

If the computer determines that all records are not yet being displayed,it proceeds by first obtaining additional position information from thedata records (box 66-3). The diff subroutine is next called upon toapply suitable algorithms to the raw data, thus generating four sets ofdistinctive values, with each set corresponding to one of the fourdisplay modes, short, long, angle, or inspection (box 66-4). Thelongitudinal and circumferential location for each of the forty-eightdetector channels are next determined by correlating signals 24, 26, and28 (box 66-5).

The predetermined threshold value for the particular display modeselected is compared to each numerical value comprising defect signal 24and, if the signal value is greater than the threshold value, a pixel isdisplayed on the CRT screen for the maximum defect value for eachlongitudinal position along the length of tubular member 22, asdisplayed on the two-dimensional map (boxes 66-6 and 66-7). If, on theother hand, the defect signal value is less than the threshold value,the signal value is ignored and the logic loop repeated.

The final key portion of the preferred program for this invention is thediff subroutine identified by flowchart 68 in FIG. 12. Since thefunction of this program is to process all numerical values containedwithin defect signal 24, it is imperative that the gain setting bematched for each of the forty-eight channel corresponding to theforty-eight separate flux detectors (box 68-1). The computer thenperforms one of five possible calculations depending upon the channelhalf width selected by the user.

If the selection is "0", the voltages for all channels are calculatedfor each discrete solid segment of tubular member 22 (boxes 68-2 and68-3). If, however, a channel half width of 1, 3, 25, or 26 is selected,the voltage values are processed according to the angle algorithm, shortalgorithm, long algorithm, or inspection algorithm, respectively, togenerate the distinctive values needed to produce the four differentdisplay modes discussed above (boxes 68-4 through 68-11).

The precise programming steps required to reproduce the preferredembodiment of the present invention will become apparent to thoseskilled in the art upon disclosure of the flowchart and the remainder ofthe specification set forth herein. It should also be understood thisspecification is by illustration only and that the invention is notnecessarily limited to the specific embodiment disclosed herein, sincealternative embodiments and operating techniques will become apparent tothose skilled in the art in view of the disclosure. Accordingly,modifications are contemplated which can be made without departing fromthe spirit of the described invention.

What I claim is:
 1. A method of determining the angular orientation of adefect in a tubular member having a longitudinal axis comprising thesteps of:providing a sensor means for detecting defects in said tubularmember; moving said sensor means and said tubular member relative to oneanother along said longitudinal axis by moving at least one of saidsensor means and said tubular member; detecting, with said sensor means,the presence of a plurality of discrete points on said defect; comparingsaid discrete points to a common frame of reference, thus establishingthe relative position of each of said discrete points with respect tothe remainder of said plurality of discrete points; correlating saidrelative position of each of said discrete points with the longitudinalorientation of said tubular member; and determining the angularorientation of said plurality of discrete points with respect to saidlongitudinal axis of said tubular member.
 2. The method of claim 1further comprising the step of displaying at a display means saidangular orientation of said plurality of discrete points.
 3. The methodof claim 1 wherein said step of detecting the presence of a plurality ofdiscrete points on said defect comprises:generating a plurality ofsignals indicative of said plurality of discrete points, wherein each ofsaid discrete points is represented by one corresponding signal; andprocessing said signals to establish the position of each of saiddiscrete points indicated by each of said signals.
 4. The method ofclaim 3 wherein said step of comparing said discrete points to a commonframe of reference comprises:establishing the point in time at whicheach of said signals indicates the presence of a corresponding discretepoint; measuring the time lag separating the detection of each adjacentdiscrete point on said defect; and applying said time lag to calculatethe relative position of each of said adjacent discrete points.
 5. Themethod of claim 1 further comprising the step of generating a timesignal, wherein said step of detecting the presence of a plurality ofdiscrete points on said defect comprises:generating a first signalindicative of a first discrete point; generating a second signalindicative of a second discrete point; and said step of comparing saiddiscrete points to a common frame of reference comprises calculating thetime lag between said first and second signals.
 6. An apparatus fordetermining the angular orientation of a defect in a tubular memberdefining a cylindrical circumferential surface, and having alongitudinal axis, comprising:sensor means for detecting the presence ofa plurality of discrete points on said defect; means cooperating withsaid sensor means for generating at least one signal indicative of saidplurality of discrete points; means for processing said at least onesignal to determine the relative position of each of said plurality ofdiscrete points with respect to said longitudinal axis of said tubularmember, and for determining the angular orientation of said defect withrespect to said longitudinal axis; and a display means, composed of aplurality of discrete points arranged in orthogonal horizontal andvertical relationship to one another, including a first axiscorresponding to the longitudinal axis of said tubular member and asecond axis corresponding to said circumferential surface, fordisplaying said defect, including said angular orientation of saiddefect.
 7. The apparatus of claim 6 further comprising clock means forgenerating a time signal, wherein:said processing means comprise acomputer for receiving and correlating said time signal and said atleast one signal indicative of said plurality of discrete points,wherein said relative position of each of said plurality of discretepoints is determined by establishing the time lag within said at leastone signal indicative of adjacent discrete points and applying said timelag to calculate the longitudinal and circumferential spacing betweensaid adjacent discrete points.
 8. The apparatus of claim 6 furthercomprising clock means for generating a time signal, wherein:said sensormeans comprises at least one first sensor for detecting the position ofa first discrete point, and at least one second sensor for detecting theposition of a second discrete point, and said signal generating meanscomprises a first means for generating a first signal indicative of saidfirst discrete point, and second means for generating a second signalindicative of said second discrete point; wherein said prpcessing meansmeasures the time lag between said first and second signals, thusdetermining the relative positions of said first and second discretepoints with respect to said longitudinal axis.